Parachutes have long been used to lower personnel to the ground from an airplane. They have also been used to provide drag to slow the speed of vehicles, for example.
More recently parachutes have been used as a safety device on small aircraft such as hang gliders, ultralight aircraft, and the like. When equipment failure causes the craft to descend to the ground the parachute is deployed to slow the fall and protect the passenger and the craft from serious injury.
One problem which has been encountered with the use of parachutes is the sudden shock to the passenger or user when the canopy of the parachute opens and fills with air quickly. This is especially serious at high speeds. Of course, the shock is greater at high speed than at low speed, and the canopy fills more rapidly at high speed. Also, in more recent years parachutes are being made with low porosity or zero porosity fabric. The opening shock with such parachutes is even more severe than was the cause with parachutes made with porous fabric.
In order to alleviate the problem of opening shock there as been proposed the use of a "line cutter". This involves a line passing through small rings attached to the base of the canopy. The length of the line used determines the diameter of the parachute when reefed. A line cutter severs this line after a predetermined time delay, allowing the parachute to completely inflate. A line cutter has the disadvantage of being time sensitive. That is, it will reef for a predetermined amount of time regardless of airspeed. They are also difficult to pressure pack. As a result, this method for reefing has not been totally satisfactory.
Another previous method involved the use of a small canopy mounted inside the main canopy. A series of lines extend from the small internal canopy to the perimeter of the main canopy. At high speed the pressure on the small canopy tensions these lines and prevents the mouth of the main canopy from expanding. This method is very sensitive to tuning and manufacturing tolerances. As a result, it has not been commercially successful. It also involves much labor in production.
Another previous method was suggested which involved the use of a small square reefing device (approximately 14 inches square). The reefing device was a membrane having a ring at each of the four corners. All of the suspension lines of the parachute extended through these rings (i.e. one-fourth of the suspension lines pass through each ring). The membrane had a center opening. This device was apparently not successful.
There has not heretofore been provided a reefing system which is efficient, effective, and reliable in slowing the opening of a parachute canopy to reduce the shock.